Needle attaching structure of rotating shaft and meter device

ABSTRACT

When a press-in part  81  is pressed-in to a press-in hole  93 , a vertex of the press-in part  81  deformed to a form along the inner surface of the press-in hole  93  comes into contact with the inner surface of the press-in hole  93  and a press-in force when the press-in part  81  is inserted into the press-in hole  93  or a pull-out force when the press-in part  81  is pulled out from the press-in hole  93  is set in according with the length of an intersecting line that a surface on which the outer surface of the press-in part  81  comes into contact with the inner surface of the press-in hole  93  and a section intersecting orthogonally to the axial direction of the press-in part  81  intersect.

BACKGROUND

1. Field of the Invention

The present invention relates to a rotating shaft to which a needle isattached that indicates numeric characters of a dial in a meter deviceof a meter of a vehicle or the like, and more particularly to a needleattaching structure of a rotating shaft in which when the needle ispressed-in to the rotating shaft, a stress is not concentrated to apart, so that the needle can be integrally attached.

2. Description of the Related Art

In such a kind of meter device to be mounted on the vehicle or the like,ordinarily, the dial in which characters, numeric characters and a scaleare provided is lighted from a back surface side by an exclusive lightsource or the needle for indicating the characters or the numericcharacters of the dial is lighted (for instance, see patent literature1).

Specifically, as such a meter device, as shown in FIG. 9, for instance,a meter device is known that includes in a meter box 102 under a dial101, a light source 103, a needle shaft 104 that guides a light from thelight source 103 and having a needle 105 attached integrally to an upperend part, bearings 106 and 107 for supporting the needle shaft 104 so asfreely rotate, a gear 108 to which a turning force form a motor notshown in the drawing is transmitted to rotate the needle shaft 104 andthe needle 105 and a parabolic shaped reflector 109 provided in a partof a light guide path in which the light from the light source 103 isguided in the needle 105, and the needle 105 is lighted by the emissionof the light from the light source 103. In the drawing, referencenumeral 110 designates a substrate.

Ordinarily, in order to provide a light guide property in the needleshaft or the needle, the needle shaft or the needle is formed with asuitable resin material and the needle is pressed-in to the needle shaftand integrally attached thereto. Accordingly, when there is a largeunevenness in working accuracy between these parts, when the needle ispressed-in to the needle shaft, since the needle is loosely attached tothe needle shaft, the needle is easily slipped out from the needleshaft. On the contrary, when the needle is tightly attached to theneedle shaft, the needle may be occasionally hardly attached to theneedle shaft. Thus, a needle attaching structure is proposed in whichparts can be assuredly attached without requiring a highly accurate work(for instance, see patent literature 2).

Namely, as shown in FIGS. 10 and 11, in the needle attaching structure,are provided a shaft part 201 made of a synthetic resin and a needleattaching part 202 formed in an upper end part of the shaft part 201 anda needle not shown in the drawing is attached to the needle attachingpart 202. In the needle, a tubular attaching fitting is provided in abottom surface (a lower surface) side as a base end. An inner part ofthe attaching fitting forms a cylindrical attaching hole H shown in FIG.12. In FIGS. 11 and 12, reference numeral 204A designates a corner partof a below-described fitting part 204. 204B designates a side part ofthe fitting part 204. 205 designates a gear.

The needle attaching part 202 has a tapered part 203 formed in an upperend part side and the straight and substantially regular square poleshaped fitting part 204 formed in a lower part side. The tapered part203 is formed so as to be smoothly fitted to an attaching hole H of theneedle and has a substantially regular square pyramid shape which isgradually thicker toward a lower side. An outer peripheral part 203A inan upper end and each corner part 203B are chamfered. On the other hand,in the fitting part 204, as shown in FIG. 12, a length s between opposedsides is formed to be slightly smaller than the inside diameter r of theattaching hole H of the needle and a length t of each diagonal line isformed so as to be slightly larger than the inside diameter r of theattaching hole H of the needle.

Patent literature 1: German Patent Application Laid-Open No. 19538547

Patent literature 2: JP-UM-A-1-120684

However, in such a needle attaching structure, when a section of thefitting part 204 in the shaft part 201 is a simple polygonal form suchas a square form, a space is largely formed between the shaft part andthe fitting part. As a result, a large quantity of light leaks from thespace, so that a rate of illuminating light guided to reach the needleis greatly reduced to deteriorate a light emitting efficiency.Especially, when a section of the fitting part has a triangular form,the space is so large as not to be neglected, so that a rate of theleakage of the light is increased. Therefore, a needle attachingstructure has been desired to be developed that can efficiently transmitthe light and realize a light emission and illumination with a goodlight emitting efficiency.

Further, in such a needle attaching structure, when the fitting parthaving a section of, for instance, a triangular form is pressed-in tothe attaching hole H of the needle, since a difference between levels ofpress-in loads of contact parts in corner parts respectively is largerthan that of non-contact parts of the corner parts which do notrespectively come into contact with the attaching hole H, there is afear that cracks are generated due to a stress concentration in thecorner parts respectively. The above-described needle attachingstructure has a problem in view of the above-described point.

SUMMARY

The present invention is devised by considering the above-describedcircumstances and it is an object of the present invention to provide aneedle attaching structure of a rotating shaft and a meter device inwhich a light emitting efficiency of a needle is not extremelydeteriorated, an illuminating light can be efficiently transmitted tothe needle and the generation of cracks can be prevented.

In order to achieve the above-described object, a needle attachingstructure of a rotating shaft according to the present invention ischaracterized by below-described (1) and (2).

(1) In a needle attaching structure of a rotating shaft in which apress-in part of the rotating shaft having light guide characteristicsis pressed-in to a press-in hole of a needle, the press-in hole has atrue circular form in section, the press-in part in an end part side ofthe rotating shaft has a regular n polygonal form in section (in thiscase, 5≦n), when the press-in part is pressed-in to the press-in hole, avertex of the press-in part deformed to a form along the inner surfaceof the press-in hole comes into contact with the inner surface of thepress-in hole and a press-in force when the press-in part is insertedinto the press-in hole or a pull-out force when the press-in part ispulled out from the press-in hole is set in according with the length ofan intersecting line that a surface on which the outer surface of thepress-in part comes into contact with the inner surface of the press-inhole and a section intersecting orthogonally to the axial direction ofthe press-in part intersect.

(2) In a needle attaching structure of a rotating shaft having thestructure of (1), the length of the intersecting line is set inaccordance with at least one of the diameter of the inner surface of thepress-in hole, a length to the vertex from an axis of the press-in partand the number n of the vertexes of the press-in part.

According to the needle attaching structure described in theabove-described (1) or (2), a space between the press-in part and thepress-in hole can be more reduced than, for instance, a case of atriangular form in section. Accordingly, the light emitting efficiencyof the needle is not seriously deteriorated by the leakage of the lightfrom the space, so that the illuminating light can be efficientlytransmitted to the needle. Further, since the press-in part has astructure that a rather large number of angular parts of a polygonalform (however, excluding too many angular parts) are respectivelydistributed to come into contact with the press-in hole, differentlyfrom the press-in part of the true circular form in section which comesinto contact with the press-in hole in an entire peripheral surface orthe press-in part of a triangular form in section which concentricallycomes into contact with the press-in hole at a small number of partssuch as three angular parts, a large press-in load can be avoided frombeing concentrically applied to the press-in hole. As a result, even inthe needle made of a synthetic resin and having a relatively lowstrength, the cracks can be prevented from being generated in thepress-in hole.

Further, the press-in load of the rotating shaft to the press-in hole isproportional to the contact area thereof, and the contact area ischanged depending on the length of the intersecting line. Accordingly,when the length of the intersecting line is adjusted (changed), thepress-in load can be set to a proper level so as not to generate thecracks in the needle sheath part and the needle can be assuredlyattached to the rotating shaft.

In order to achieve the above-described object, a meter device accordingto the present invention is characterized by below-described (3) and(4).

(3) In a meter device comprising:

a display plate;

a rotating shaft that has an end part protruding to a front surface sidefrom the display plate and rotates by a turning force transmitted from amotor through a gear;

a needle that has in a lower surface a press-in hole to which a press-inpart in the end part side of the rotating shaft is pressed-in androtates along the front surface side of the display plate; and

a light source that is provided in a back surface side of the displayplate and outputs an illuminating light advancing in the rotating shaftfrom a base end part to the end part to emit the light from the needle,the rotating shaft having light guide characteristics is pressed-in tothe press-in hole of the needle, the press-in hole has a true circularform in section, the press-in part in the end part side of the rotatingshaft has a regular n polygonal form in section (in this case, 5≦n),when the press-in part is pressed-in to the press-in hole, a vertex ofthe press-in part deformed to a form along the inner surface of thepress-in hole comes into contact with the inner surface of the press-inhole and a press-in force when the press-in part is inserted into thepress-in hole or a pull-out force when the press-in part is pulled outfrom the press-in hole is set in according with the length of anintersecting line that a surface on which the outer surface of thepress-in part comes into contact with the inner surface of the press-inhole and a section intersecting orthogonally to the axial direction ofthe press-in part intersect.

(4) In a meter device having the structure of (3), the length of theintersecting line is set in accordance with at least one of the diameterof the inner surface of the press-in hole, a length from an axis to thevertex of the press-in part and the number n of the vertexes of thepress-in part.

According to the meter device described in the above-described (3) or(4), the light emitting efficiency of the needle is not seriouslydeteriorated because of the same reason, so that the illuminating lightcan be efficiently transmitted to the needle and the generation of thecracks can be prevented. Further, the length of the intersecting line isadjusted (changed), so that the press-in load can be set to a properlevel so as not to generate the cracks in the needle sheath part and theneedle can be assuredly attached to the rotating shaft.

According to the needle attaching structure of the rotating shaft andthe meter device of the present invention, the space between thepress-in part and the press-in hole can be more reduced than, forinstance, a case of a triangular form in section. Accordingly, the lightemitting efficiency of the needle is not seriously deteriorated by theleakage of the light from the space, so that the illuminating light canbe efficiently transmitted to the needle. Further, since the press-inpart has a structure that only a rather large number of angular parts ofa polygonal form respectively come into contact with the press-in hole,differently from the press-in part of the true circular form in sectionwhich comes into contact with the press-in hole in an entire peripheralsurface or the press-in part of a triangular form in section whichconcentrically comes into contact with the press-in hole at a smallnumber of parts such as three angular parts, a large press-in load canbe avoided from being concentrically applied to the press-in hole. Thus,even in the needle made of a synthetic resin and having a relatively lowstrength, the cracks can be advantageously prevented from beinggenerated in the press-in hole.

Further, the press-in load of the rotating shaft to the press-in hole isproportional to the contact area thereof, and the contact area ischanged depending on the length of the intersecting line in which eachvertex of the rotating shaft comes into contact with the innerperipheral surface of the press-in hole. Accordingly, when the length ofthe intersecting line is adjusted (changed), the press-in load can bepreferably set to a proper level so as not to generate the cracks in theneedle sheath part and the needle can be advantageously assuredlyattached to the rotating shaft.

The present invention is briefly described above. Further, an exemplaryembodiment for embodying the present invention will be read by referringto the attached drawings to more clarify a detail of the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view showing a meter device to which aneedle attaching structure of a rotating shaft according to an exemplaryembodiment of the present invention is applied.

FIG. 2 is a sectional view of the meter device.

FIG. 3(A) is an explanatory view showing a state before a press-in partin the meter device shown in FIG. 2 is pressed-in to a press-in hole,and FIG. 3(B) is an explanatory view showing a state after thepressing-in operation.

FIG. 4 is a sectional view taken along a line IV-IV in FIG. 3(B).

FIG. 5 is an explanatory view, in a comparative example, showing a statethat a press-in part having a section of a triangular form is pressed-into a press-in hole.

FIG. 6 is an explanatory view, in another comparative example, showing astate that a press-in part having a section of a true circular form ispressed-in to a press-in hole.

FIG. 7 is an explanatory view showing a length of a circumference of afitting part of the rotating shaft and a sheath part of a needle in theexemplary embodiment of the present invention.

FIG. 8 is an explanatory view showing another length of thecircumference of the fitting part of the rotating shaft and the sheathpart of the needle in the exemplary embodiment of the present invention.

FIG. 9 is a sectional view of a meter device using a usual needleattaching structure.

FIG. 10(A) is an explanatory view showing a rotating shaft to whichanother usual needle attaching structure is applied and FIG. 10(B) is anenlarged view of main parts thereof.

FIG. 11 is a plan view of FIG. 10(B).

FIG. 12 is an explanatory view showing a relation of sizes of a fittingpart of the rotating shaft shown in FIG. 10 and an attaching hole.

DETAILED DESCRIPTION

Now, an exemplary embodiment of the present invention will be describedbelow in detail by referring to the attached drawings.

FIGS. 1 and 2 show a meter device 1 having a rotating shaft to which aneedle attaching structure of the present invention is applied.

The meter device 1 includes a light source 3 mounted on a substrate 2, ameter case 4 attached to a prescribed position on the substrate 2including an area where the light source 3 is mounted and a displayplate not shown in the drawing that is arranged on the meter case 4 anddisplays necessary information about a vehicle itself or an environmentin the periphery of the vehicle such as numeric characters, characters,signs or the like.

The meter device 1 of the present exemplary embodiment forms a part of acombination meter not shown in the drawing. The display plate forming afront surface side is fitted to an entire surface to form a reverseplate. Further, in the display plate, various kinds of display windowsare opened for installing various kinds of meters including the meterdevice 1 and formed integrally with a combination meter case formingside surface and back surface sides. Further, the display plate has anupper part covered with a transparent cover glass of a black color thatis not shown in the drawing.

The meter device 1 of the present exemplary embodiment forms a speedmeter, and a needle 9 is rotated by a prescribed angle in accordancewith a sensor signal corresponding to a present speed detected by asensor not shown in the drawing to indicate a specific numeric characterformed in the display plate not shown in the drawing. Thus, the presentspeed is analog displayed.

The light source 3 of the present exemplary embodiment is formed with,for instance, an LED (Light Emitting Diode) for outputting a visiblelight of a prescribed wavelength (λ). As a light (refer it to as anilluminating light, hereinafter) outputted from the light source 3, theilluminating light is used that has no dependence on a direction over aphase angle of 360° and uniform output characteristics. Namely, thelight source 3 of the present exemplary embodiment has light quantitydistribution characteristics that output a substantially uniformquantity of light to a rotating shaft 8 over an entire circumferencewith respect to a horizontal plane (a X-Y plane).

The light source 3 of the present exemplary embodiment is not especiallylimited to the LED, and a compact point light source whose consumedelectric power is low is preferable.

The meter case 4 includes a lower case 4A fixed to the substrate 2 andan upper case 4B laminated on and screwed to the lower case 4A. In themeter case 4, the rotating shaft 8 is provided that has a motor 5, anintermediate gear 6 and an output gear 7 integrally formed. To an endpart (refer it also to as an “upper end part”, hereinafter) of therotating shaft 8 partly protruding outside the meter case 4, a needle 9is pressed-in. In the rotating shaft 8, a brake spring 11 is interposed.

The motor 5 serves to rotate the needle 9 and rotates the rotating shaft8 through the intermediate gear 6 and the output gear 7 to rotate theneedle 9 along the surface of the display plate and indicate variouskinds of necessary information. The motor 5 of the present exemplaryembodiment includes a stator 51 made of a suitable electricallyconductive material and a rotor 52 attached to a rotor shaft 52A in anopened inner part of the stator 51, and forms a stepper motor.

The stator 51 is fixed to the lower case 4A, a magnetic core as amagnetic pole protrudes in the opened inner part and a coil 51A wound ona bobbin is attached to the magnetic core.

The rotor 52 is configured in a substantially cylindrical form by asuitable magnetic material and provided in the opened inner part of thestator 51 so as to freely rotate. To an upper part of the rotor, a rotorgear 53 is coaxially fixed. The rotor shaft 52A to which the rotor 52 isattached is supported by a bearing 52B (see FIG. 2) provided in thelower case 4A so as to freely rotate.

The intermediate gear 6 is fixed to a support shaft 6A and the supportshaft 6A is supported by a bearing 6B provided in the lower case 4A soas to freely rotate. In the intermediate gear 6, a large gear 61 havingthe large number of teeth provided in an outer periphery mesh with therotor gear 53 having the small number of teeth provided in the upperpart of the rotor 5, so that a rotating speed (a turning force) from therotor 52 is decelerated and transmitted to the intermediate gear 6.Further, to the intermediate gear 6, a pinion 62 having the small numberof teeth and a small diameter is fixed coaxially and integrally with thesupport shaft 6A.

The output gear 7 is formed integrally with the rotating shaft 8 in anintermediate part of the rotating shaft 8 to transmit the turning forcefrom the pinion 62 of the intermediate gear 6 to the rotating shaft 8.Especially, the output gear 7 is formed with a suitable resin materialexcellent in its light guide characteristics in order to avoid a part ofthe illuminating light incident from the light source 3 facing a baseend part (refer it to as a “lower end part”, hereinafter) of thebelow-described rotating shaft 8 that advances to the output gear 7 frombeing damped or absorbed in the output gear 7.

Further, in the output gear 7, in order to suppress a surface area of aconnecting part to the rotating shaft 8 to a minimum value as low aspossible, a thickness (t) of the output gear 7 is reduced to a value assmall as possible under a condition that a prescribed strength isassured. Thus, a structure is obtained that a loss of the illuminatinglight due to the advancement of the light from the rotating shaft 8 tothe output gear 7 can be suppressed to a minimum level. On an uppersurface of the output gear 7, an initial position setting pin 72 standsupright that is engaged with a stopper surface 42 (see FIG. 2) of theupper case 4B.

Further, in the output shaft 7, a large gear 71 having the large numberof teeth provided on an outer periphery meshes with the pinion 62provided on an upper part of the intermediate gear 6, so that therotating speed of the intermediate gear 6 is more decelerated andtransmitted to the output gear 7 to rotate the output gear 7. Therotating shaft 8 in contact with the output gear 7 is rotated integrallywith the output gear 7 whose rotating speed is greatly decelerated atthe same angular velocity.

The rotating shaft 8 is configured in a solid and substantiallycylindrical shape formed integrally with the output gear 7 by a suitablelight transmitting resin material excellent in its light guidecharacteristics. Further, as described above, in the rotating shaft 8,the upper end part side protrudes to an outer part of the meter case 4from a shaft hole 41 of the upper case 4B and protrudes on the surfaceof the display plate. In the rotating shaft 8, to the upper end part,the needle 9 is attached, and the lower end part is supported by abearing 8A provided in the lower case 4A so as to freely rotate.

Further, a lower end surface of the rotating shaft 8 is provided to belocated just above the light source 3 as shown in FIG. 2. When theilluminating light from the light source 3 is incident thereon, theilluminating light is guided in the rotating shaft 8 and transmitted tothe upper end part. Accordingly, in the rotating shaft 8, in aninterface part of an inner part and an outer peripheral surface, most ofthe illuminating lights are reflected (for instance, a regularreflection or a total reflection or the like) to advance to the upperend part.

Further, the rotating shaft 8 has, as shown in FIG. 3, from the upperend of the rotating shaft 8, a press-in part 81 formed with a section ofa polygonal form by at least a length a corresponding to the depth a ofa below-described press-in hole 93 of the needle 9. The press-in part 81in the present exemplary embodiment has a section of a regular hexagonalform as shown in FIG. 4. If the light leaks from the press-in part 81 toan outer part, that is, a space β facing the press-in hole 93 of theneedle 9, since the width of the space is small, a quantity of theleakage of the light can be suppressed to a level as low as possible.

Further, in the press-in part 81, at least a maximum diagonal line ofthe regular hexagonal form in section before the press-in part isallowed to be pressed-in to the press-in hole has a dimension slightlylarger than a diameter D of the press-in hole 93 before the press-inpart is pressed-in to the press-in hole. Here, the “maximum diagonalline” is geometrically defined as a diagonal line having a maximumlength for connecting together two regularly opposed vertexes of twomutually opposed vertexes, specifically, the two vertexes separated witha central angle of 180° in the case of the regular hexagonal form.

In the present exemplary embodiment, a sectional form of the press-inpart 81 is configured in the regular hexagon, however, the sectionalform is not especially limited thereto. An n polygonal form in sectionmay be used in which the number n of side parts and angular parts(vertexes) is located within a range expressed by 3≦n≦10, andespecially, the number n of the side parts and the angular parts ispreferably located within a range expressed by 6≦n≦8. As describedabove, in the present exemplary embodiment, the sectional form of thepress-in part 81 is configured to be a sectional form in which thenumber n of the side parts and the angular parts (the vertexes) islocated within the range expressed by 6≦n≦8 and to be a polygonal formin section in which the number of the vertexes is large to some degree.Thus, when the press-in part is pressed-in to the press-in hole 93 ofthe needle 9, a stress by angular parts (parts corresponding to thevertexes of the regular hexagonal form) 81A of the press-in part 81 canbe distributed as much as possible and an unevenness in the stress bythe angular parts 81A can be reduced as much as possible. A scatteredlight or the leakage of light caused by a below-described space (seeFIG. 4) between the press-in part 81 and the press-in hole 93 isrestrained from occurring.

The needle 9 includes a needle sheath part (hub) 91 with the press-inhole 93 formed to which the rotating shaft 8 is pressed-in, a deflectingsurface 94 formed in a boundary part to the needle sheath part 91 and apointer part 92 for indicating a design part such as a scale, and isintegrally formed with a suitable resin material having suitable lightguide characteristics. Thus, the illuminating light guided from therotating shaft 8 is guided to the needle sheath part 91 and the pointerpart 92. Further, a head part (an upper part) of the needle sheath part91 of the needle 9 is covered with a cap 12.

The press-in hole 93 of the needle sheath part 91 is opened to a lowersurface of the needle sheath part 91, and its sectional form issubstantially circular (especially, a true circular form). The needlesheath part 91 has a prescribed dimension of an inside diameter in whichthe angular parts 81A respectively come into contact with the press-inhole 93 when the press-in part 81 of the rotating shaft 8 is pressed-into the press-in hole 93. Namely, the inside diameter D of the press-inhole 93 of the present exemplary embodiment is dimensionally worked sothat the inside diameter D is slightly smaller than a dimension of themaximum diagonal line for connecting together the regularly opposedangular parts 81A of the press-in part 81 of the rotating shaft 8.

The deflecting surface 94 of the pointer part 92 serves to deflect theoptical paths of most of the illuminating lights incident on the needlesheath part 91 through the press-in hole 93 from the upper part of therotating shaft 8 and advance the illuminating lights to the pointer part92. As shown in FIG. 3(B), the deflecting surface 94 is formed by aninclined surface inclined by a prescribed angle ⊖ (for instance, 45°)with respect to a central axis A of the rotating shaft 8 and thepress-in hole 93 of the needle sheath part 91.

The cap 12 is provided to avoid the light from the light source 3 frombeing directly incident on the eye of a person who visually recognizes adisplay. Even when the illuminating light passing through the needlesheath part 91 passes through the needle sheath part 91 to be incidenton the cap 12, the illuminating light is absorbed by the cap to preventthe illuminating light from being directly transmitted upward. Sincemost of the illuminating lights advancing in the needle sheath part 91are not incident on the cap 12 and the optical path thereof is deflectedby the deflecting surface 94, the illuminating lights can be effectivelymoved forward to the pointer part 92.

Now, an operation of the present exemplary embodiment will be describedbelow. Here, in the description of the meter device 1, the speed meterof various meters is exemplified and an operation thereof is described,however, the present invention is not especially limited thereto. Theoperation is the same as that of other analog type meter device.

The motor 5 provided in the meter case 4 of the meter device 1 isrotated and driven in accordance with the sensor signal corresponding tothe present speed detected by the sensor not shown in the drawing torotate the needle not shown in the drawing by a prescribed angle andindicate a specific numeric character formed on the display plate notshown in the drawing.

Namely, in the meter device 1 of the present exemplary embodiment, thesensor signal corresponding to the speed detected by the sensor notshown in the drawing is transmitted to the coil 51A of the stator 51side shown in FIG. 1 to generate a magnetic force in the magnetic coreas each magnetic pole and the rotor 52 is rotated by the magnetic force.

Thus, as shown in FIG. 2, the turning force is decelerated andtransmitted to the large gear 61 of the intermediate gear 6 from therotor gear 53 formed integrally with the rotor 52 to rotate theintermediate gear 6 and the support shaft 6A supporting the intermediategear 6 at a prescribed angular velocity. Then, from the pinion 62 of therotating intermediate gear 6, the turning force is more decelerated andtransmitted to the output gear 7 and the rotating shaft 8 to rotate theoutput gear 7 and the rotating shaft 8 formed integrally therewith at aprescribed angular velocity. Thus, the needle 9 attached to the upperend part of the rotating shaft 8 is rotated by a prescribed angle toindicate the specific numeric character on the display plate by an endpart of the pointer part 92 of the needle 9. Thus, the present speed canbe analog displayed to inform a driver of the present speed.

On the other hand, in the meter device 1 that displays the speed, theilluminating lights substantially equally outputted over an entirecircumference of 360° from the light source 3 enter from an incidentsurface as the lower end part of the rotating shaft 8 arranged justabove the light source 3, as shown in FIG. 2. Thus, most of theilluminating lights incident on the rotating shaft 8 from the incidentsurface are repeatedly reflected in the interface part of the inner partand the outer peripheral surface of the rotating shaft 8 and advanceupward in the rotating shaft 8.

A part of the illuminating lights entering from the incident surface asthe lower end part of the rotating shaft 8 may be occasionally incidenton the inner part of the output gear 7 from the intermediate connectingpart to the output gear 7, move forward and leak outside. However, sincethe thickness of the output gear 7 is reduced as much as possible, aphenomenon of the leakage of the light can be suppressed as much aspossible.

As described above, the illuminating light repeats a transmissionphenomenon that the illuminating light is incident on the outerperipheral surface in the inner part of the rotting shaft 8, similarlyreflected and advance upward, and finally, is incident on an inner partof the needle sheath part 91 through the press-in hole 93 of the needle9 from the upper end part of the rotating shaft 8. The illuminatinglight incident on the needle sheath part 91 further advances to thepointer part 92 formed integrally with the needle sheath part 91. Theoptical paths of most of the illuminating lights are deflected by thedeflecting surface 94 so that the end part of the needle 9 and a part inthe vicinity thereof can be lighted by emitting the light. It is to beunderstood that such a transmitting operation of the illuminating lightin the rotating shaft 8 is carried out even during the rotatingoperation of the rotating shaft 8 without a change as in the case of astationary state except that the optical path is rotated spirallyupward.

While the illuminating lights are moving forward in the rotating shaft8, a part of the lights may possibly leak in the connecting part to theoutput gear 7, however, in the present exemplary embodiment, thethickness f the output gear 7 is reduced as much as possible.Accordingly, a quantity of the light is suppressed that moves forward tothe output gear 7 from the connecting part and leaks outside from theoutput gear.

Therefore, according to the needle attaching structure of the rotatingshaft 8 of the present exemplary embodiment, the press-in part 81provided in the upper part of the rotating shaft 8 is configured in theregular hexagonal form in section. Accordingly, the space between thepress-in part 81 of the rotating shaft 8 and the press-in hole 93 of theneedle sheath part 91 in the present exemplary embodiment is moregreatly reduced than a space between a press-in part of a rotating shaft20A and a press-in hole 93 of a needle sheath part 91 in the case of aneedle attaching structure using the rotating shaft 20A having thepress-in part of an equilateral triangular form in section as in acomparative example shown in FIG. 5. A rate of the illuminating lightleaking from the space is the more suppressed and a light transmittingefficiency can be improved.

Further, for instance, as a comparative example shown in FIG. 6, when apress-in part in an upper end side of a rotating shaft 20B has a truecircular form in section and has an outside diameter gradually increasedtoward a lower end part, a large press-in force is necessary during apress-in work and a high working accuracy is required for the press-inpart of the rotating shaft 20B and a press-in hole 93 of a needle sheathpart 91. As a result, there is a fear that a tolerance is hardlymanaged, which is apt to cause a cost to increase. Further, in thiscase, there is a fear that such a stress as to pull the needle sheathpart 91 in the circumferential direction shown by arrow marks acts togenerate cracks.

On the other hand, according to the needle attaching structure of therotating shaft 8 of the present exemplary embodiment, the rotating shaft8 or the needle 9 is formed with a synthetic resin by considering thelight guide characteristics. When the rotating shaft 8 or the needle 9is formed with the resin, the working accuracy is lower than that whenthe rotating shaft or the needle is formed with metal. By consideringsuch circumstances, the press-in part 81 of the rotating shaft 8 isconfigured in the regular hexagonal form in section. Accordingly, evenwhen there is an unevenness in work to some degree in the press-in part81 of the rotating shaft 8 or the press-in hole 93 of the needle sheathpart 91, since only the angular parts 81A of the press-in part 81 partlycome into contact with an inner peripheral surface of the press-in hole93, the angular parts 81A operate just like a guide so that the press-inpart 81 is merely pressed in to the press-in hole 93 along the angularparts. Thus, the large press-in force is not necessary during thepress-in work. Namely, since contact points of the angular parts 81Aserve to press and bend the press-in hole 93 outward in the radialdirection as shown in arrow marks, the generation of the cracks isprevented.

Further, according to the present exemplary embodiment, as shown in FIG.4, a press-in structure is used in which the angular parts 81A of thepress-in part 81 are distributed at equal intervals to come into contactwith the press-in hole so that the angular parts 81A of the press-inpart 81 iso-metrically come into contact with the inner peripheralsurface of the pressure-in hole 93 at regular intervals of 60°.Accordingly, a stress is avoided from being partly and excessivelyconcentrated and the generation of the cracks in the needle 9 can beeffectively suppressed.

Further, according to the present exemplary embodiment, since thepress-in part 81 of the rotating shaft 8 is configured in the regularhexagonal form in section, in other words, the sectional form of thepress-in part 81 avoids a structure of a polygonal form having too manyside parts and angular parts. Accordingly, the occurrence of irregularreflection due to many scattered lights of leaking lights in the spacebetween the press-in part 81 and the press-in hole 93 can be prevented.Thus, a calm and moderate lighting effect can be the more realizedwithout a glare of high luminance.

As described above, in the sectional form of the press-in part 81 havingthe polygonal form, the number n of the side parts and the angular parts81A is located within a range expressed by 3≦n≦10, and preferablylocated within a range expressed by 6≦n≦8. In this case, the angularparts 81A of the press-in part 81 respectively reduce the unevenness inthe stress applied to the inner peripheral surface of the press-in hole93 in the needle sheath part 91, so that the stress can be avoided frombeing concentrated on a part of the inner peripheral surface of thepress-in hole 93. Accordingly, the stress is averaged in all the innerperipheral surface of the press-in hole 93 and the press-in force of thepress-in part 81 to the press-in hole 93 can be adjusted to a suitablelevel so as not to cause damage such as the cracks in the needle sheathpart 91. Further, the illuminating lights passing through the rotatingshaft 8 can be restrained from being scattered or leaking, which iscaused by the space between the press-in part 81 and the press-in hole93. A below-described effect can be anticipated as well as theabove-described effects. Namely, the number of the angular parts 81A ofthe press-in part 81 is increased or decreased to change a length of acircumference of a fitting part in the angular part 81A of the rotatingshaft 8 to the needle sheath part 91. Thus, the press-in force of therotating shaft 8 to the press-in hole 93 can be adjusted. When thepress-in force is properly adjusted, the cracks can be avoided frombeing generated in the needle sheath part 91.

By referring to FIGS. 7 and 8, a method for adjusting the press-in forcewill be described below. FIG. 7 shows a case that a regular hexagonalpole shaped rotating shaft 8 having six angular parts 81A (the number nof the angular parts 81A is expressed by n=6) in the press-in part 81 isconnected to the needle sheath part 91. In this case, the press-in part81 of the rotating shaft 8 is inserted into the press-in hole 93 of theneedle sheath part 91. Here, a case is described in which a material ofthe needle sheath part 91 is a little harder than a material of therotating shaft 8.

As shown in FIG. 7, a case is considered that the angular part 81A ofthe press-in part 81 is larger than the inside diameter of the press-inhole 93, namely, a case that when an axis of the rotating shaft 8 and anaxis of the needle sheath part 91 are arranged on the same straightline, the vertex of the angular part 81A of the press-in part 81 islocated outside an inner surface that defines the press-in hole 93 ofthe needle sheath part 91. As shown in FIG. 3, in order to improve aneasy insertion of the press-in part 81 into the press-in hole 93, alower end of the press-in hole 93 near the opening of the inner surfaceis tapered. The inside diameter of the press-in hole 93 indicates aninside diameter in an upper end located at a position deeper than thetapered lower end.

In this case, when the press-in part 81 is inserted into the press-inhole 93, the angular part 81A of the press-in part 81 comes into contactwith the inner surface of the press-in hole 93 formed to be tapered asshown in FIG. 3. Here, when the press-in part 81 is pressed-in to thepress-in hole 93, the angular part 81A of the press-in part 81 iscollapsed by the inner peripheral surface of the press-in hole 93. Thecollapsed part (a part shown by a chain line in FIG. 7 corresponds tothe collapsed part.) is expanded along the inner surface of the press-inhole 93 (along a circular arc surface in section) in both sides (rightand left sides in the drawing) of a contact part of the press-in part 81and the press-in hole 93. Since an external force for deforming thepress-in part 81 is required and a frictional force between the outersurface of the press-in part 81 and the inner surface of the press-inhole 93 is large in accordance with the deformation, the press-in forcenecessary for inserting the press-in part 81 into the press-in hole 93is more increased as the press-in part 81 is more deeply inserted.

Here, as described above, the length of the position where the angularpart 81A of the rotating shaft 8 is collapsed to come into contact withthe inner surface of the press-in hole 93 along the circular arc surfaceis defined as the “length of the circumference of the fitting part” (seeX1 in FIG. 7 and X2 in FIG. 8). More specifically, the length of theposition along the circular arc surface is defined as a length of anintersecting line that a surface on which the outer surface of thepress-in part 81 comes into contact with the inner surface of thepress-in hole 93 and a section intersecting orthogonally to the axialdirection of the press-in part 81 intersect. A dimension of the lengthof the circumference of the fitting part corresponds to the size of acontact area of the press-in part 81 of the rotating shaft 8 and thepress-in hole 93 of the needle sheath part 91. As a result, the lengthof the circumference of the fitting part may give an influence to thelevel of the press-in force necessary for inserting the press-in part 81into the press-in hole 93 (a study, will be described below, of arelation between the size of the contact area of the press-in part 81 ofthe rotating shaft 8 and the press-in hole 93 of the needle sheath part91 and the level of the press-in force necessary for inserting thepress-in part 81 into the press-in hole 93). Accordingly, when thelength of the circumference of the fitting part of the collapsed part isadjusted to a suitable dimension, the press-in force can be set to aproper press-in force in which the cracks or damage are not generated inthe needle sheath part 91 and a proper holding force can be provided bywhich the needle sheath part 91 does not slip out from the rotatingshaft 8 after the press-in part 81 is inserted in to the press-in hole93.

FIG. 8 shows a case that a rotating shaft 8 of a regular octagonal formin section (an octagon pole) having eight angular parts 81A more thanthe number of the angular parts 81A of the rotating shaft 8 shown inFIG. 7 (the number n of the angular parts 81A is expressed by n=8) isconnected to the needle sheath part 91. In this case, when the press-inpart 81 is inserted into the press-in hole 93, the angular part 81A ofthe press-in part 81 comes into contact with the inner surface of thepress-in hole 93 formed to be tapered as shown in FIG. 3. Here, when thepress-in part 81 is pressed-in to the press-in hole 93, the angular part81A of the press-in part 81 is collapsed by the inner peripheral surfaceof the press-in hole 93. The collapsed part (a part shown by a chainline in FIG. 8 corresponds to the collapsed part.) is expanded in bothsides (right and left sides in the drawing) of a contact part of thepress-in part 81 and the press-in hole 93 along a circular arc surfaceof the press-in hole 93. Since an external force for deforming thepress-in part 81 is required and a frictional force between the outersurface of the press-in part 81 and the inner surface of the press-inhole 93 is increased in accordance with the deformation, the press-inforce necessary for inserting the press-in part 81 into the press-inhole 93 is more increased as the press-in part 81 is more deeplyinserted.

As understood from the comparison of FIG. 7 with FIG. 8, when the numberof the angular parts 81A of the rotating shaft 8 is increased, thelength of the circumference of the fitting part is more increased(X2>X1). In such a way, even when a maximum radius of the rotating shaft8 (a length to the angular part 81A from an axis) is not changed, if thenumber of the angular parts 81A is increased or decreased, the length ofthe circumference of the fitting part can be adjusted. This means thatwhen the number of the angular parts 81A is increased or decreased, thepress-in force necessary for pressing-in the rotating shat 8 to thepress-in hole 93 can be adjusted.

As shown in FIG. 4, the present invention has the press-in structure inwhich the angular parts 81A of the press-in part 81 are distributed atequal intervals to come into contact with the press-in hole so that theangular parts 81A of the press-in part 81 iso-metrically come intocontact with the inner peripheral surface of the pressure-in hole 93 atregular intervals of 60°. Accordingly, a stress is avoided from beingpartly and excessively concentrated and the generation of the cracks inthe needle 9 can be effectively suppressed. In addition thereto, thelength of the circumference of the fitting part of the collapsed part ofthe rotating shaft 8 can be adjusted by the number of the angular parts81A so that the press-in force necessary for pressing-in the rotatingshaft 8 to the press-in hole 93 may be adjusted.

As described in the examples compared by referring to FIGS. 7 and 8, inorder to adjust the length of the circumference of the fitting part, thenumber of the angular parts 81A of the rotating shaft 8 is increased ordecreased. It is to be understood that the length of the circumferenceof the fitting part can be adjusted by increasing or decreasing themaximum radius of the rotating shaft 8 (the length to the angular part81A from the axis) or by increasing or decreasing the diameter of thepress-in hole 93 of the needle sheath part 91.

Now, a relation between the size of the contact area of the press-inpart 81 of the rotating shaft 8 and the press-in hole 93 of the needlesheath part 91 and the level of the press-in force necessary forinserting the press-in part 81 into the press-in hole 93 will be takeninto consideration.

When the entire surface of the outer surface of the rotating shaft 8having a circular section abuts on the inner surface of the press-inhole 93, assuming that a diameter of the rotating shaft is Ds, a fittinglength (a length in a direction of depth where the rotating shaft 8comes into contact with the press-in hole 93) is L, a contact facepressure is P and a coefficient of friction is μ, the press-in force Fof the rotating shaft 8 to the needle sheath part 91 is expressed by anequation (1).

F=π×Ds×L×P×μ  (1)

Here, since π×Ds×L indicates the contact area of the rotating shaft 8and the needle sheath part 91, it is understood that the press-in forceF is proportional to the contact area when the contact face pressure Pis not changed.

It may be said from the equation (1) that the press-in force F isproportional to the contact area of the press-in part 81 of the rotatingshaft 8 and the press-in hole 93 and the needle sheath part 91. Further,in the present exemplary embodiment in which the press-in part 81 comesinto contact with the press-in hole 93 at the parts of the number of theangular parts 81A, since the contact area is expressed by (the number ofthe angular parts (81A)×(the length of the circumference of the fittingpart)×(the fitting length), the press-in force F may be said to beproportional to the product of the number of the angular parts 81A andthe length of the circumference of the fitting part.

As described above, since the number of the angular parts 81A isincreased or decreased, the maximum radius of the rotating shaft 8 (thelength to the angular part 81A from the axis) is increased or decreasedor the diameter of the press-in hole 93 of the needle sheath part 91 isincreased or decreased, so that the length of the circumference of thefitting part can be adjusted, the press-in force necessary forpressing-in the rotating shaft 8 to the press-in hole 93 can be adjustedby suitably increasing or decreasing these figures. For instance, asshown in FIGS. 7 and 8, if the length of the circumference of thefitting part is changed to X2 from X1 by increasing the number of theangular parts 81A of the rotating shaft 8 to 8 from 6, a press-in forceF2 necessary for inserting the press-in part 81 of the rotating shaft 8having eight angular parts 81A into the press-in hole 93 is(8/6)×(X2/X1) times as large as a press-in force F1 necessary forinserting the press-in part 81 of the rotating shaft 8 having sixangular parts 81A into the press-in hole 93 (when it is assumed that arepulsion force due to the deformation of the rotating shaft 8 isfixed). Further, for instance, if the maximum radius of the rotatingshaft 8 (the length to the angular part 81A from the axis) is increasedor decreased or the diameter of the press-in hole 93 of the needlesheath part 91 is increased or decreased so that the length of thecircumference of the fitting part is changed to X4 from X3, a press-inforce F4 necessary for inserting the press-in part 81 of the rotatingshaft 8 when the length of the circumference of the fitting part is X4into the press-in hole 93 is (X2/X1) times as large as a press-in forceF3 necessary for inserting the press-in part 81 of the rotating shaft 8when the length of the circumference of the fitting part is X3 into thepress-in hole 93 (when it is assumed that a repulsion force due to thedeformation of the rotating shaft 8 is fixed).

The proper press-in force is to be set (adjusted) by considering thedimensional tolerance of the rotating shaft 8 and the needle sheath part91 and the temperature change of a peripheral environment and preferablydetermined in accordance with an upper limit value and a lower limitvalue of the length of the circumference of the fitting part calculatedby using experimental (measured) data or a theoretical equation of thedimensional tolerance and the temperature change.

As described above, in the needle attaching structure of the rotatingshaft 8 of the exemplary embodiment of the resent invention, the numberof the angular parts 81A of the press-in part 81 is suitably increasedor decreased to adjust the length of the circumference of the fittingpart of the press-in part 81 fitted to the press-in hole 93 of theneedle sheath part 91 so that the contact area of the press-in part 81to the press-in hole 93 may be adjusted. Thus, the press-in forcenecessary for pressing-in the rotating shaft 8 to the press-in hole 93can be adjusted.

In the exemplary embodiment of the present invention, an adjustment ofthe load when the rotating shaft 8 is pressed-in to the needle sheathpart 91 is described. Further, a pull-out force for pulling out therotating shaft 8 from the needle-sheath part 91 can be adjusted at thesame time by adjusting the press-in force in the present invention.

The present invention is not limited to the above-described exemplaryembodiment and various kinds of forms may be embodied within a scopewithout departing from the gist of the invention. Namely, the meterdevice having the rotating shaft to which the needle attaching structureof the present invention is applied may be applied to various kinds ofmeters such as a fuel gauge part, a speed meter part and a watertemperature gauge.

1. A needle attaching structure of a rotating shaft in which a press-inpart of the rotating shaft having light guide characteristics ispressed-in to a press-in hole of a needle, wherein the press-in hole hasa true circular form in section, the press-in part in an end part sideof the rotating shaft has a regular n polygonal form in section (in thiscase, 5≦n), when the press-in part is pressed-in to the press-in hole, avertex of the press-in part deformed to a form along the inner surfaceof the press-in hole comes into contact with the inner surface of thepress-in hole, and a press-in force when the press-in part is insertedinto the press-in hole or a pull-out force when the press-in part ispulled out from the press-in hole is set in according with the length ofan intersecting line that a surface on which the outer surface of thepress-in part comes into contact with the inner surface of the press-inhole and a section intersecting orthogonally to the axial direction ofthe press-in part intersect.
 2. The needle attaching structure of therotating shaft according to claim 1, wherein the length of theintersecting line is set in accordance with at least one of the diameterof the inner surface of the press-in hole, a length to the vertex froman axis of the press-in part and the number n of the vertexes of thepress-in part.
 3. A meter device comprising: a display plate; a rotatingshaft that has an end part protruding to a front surface side from thedisplay plate and rotates by a turning force transmitted from a motorthrough a gear; a needle that has in a lower surface a press-in hole towhich a press-in part in the end part side of the rotating shaft ispressed-in and rotates along the front surface side of the displayplate; and a light source that is provided in a back surface side of thedisplay plate and outputs an illuminating light advancing in therotating shaft from a base end part to the end part to emit the lightfrom the needle, wherein the rotating shaft having light guidecharacteristics is pressed-in to the press-in hole of the needle, thepress-in hole has a true circular form in section, the press-in part inthe end part side of the rotating shaft has a regular n polygonal formin section (in this case, 5≦n), when the press-in part is pressed-in tothe press-in hole, a vertex of the press-in part deformed to a formalong the inner surface of the press-in hole comes into contact with theinner surface of the press-in hole, and a press-in force when thepress-in part is inserted into the press-in hole or a pull-out forcewhen the press-in part is pulled out from the press-in hole is set inaccording with the length of an intersecting line that a surface onwhich the outer surface of the press-in part comes into contact with theinner surface of the press-in hole and a section intersectingorthogonally to the axial direction of the press-in part intersect. 4.The meter device according to claim 3, wherein the length of theintersecting line is set in accordance with at least one of the diameterof the inner surface of the press-in hole, a length from an axis to thevertex of the press-in part and the number n of the vertexes of thepress-in part.